For those of you who have had a few dozen (or more) colleagues over the years, how do you "maintain" your professional network?
Some things I've tried are:
Look forward to hearing what has worked for you...
I don't have a great answer, but I think it's a great question :)
In my experience, most people do a really bad job of this -- it's easy to forget about past relationships, and the default ending state of most work relationships is that they peter out without consistent effort. A few thoughts on what the options you suggested:
Another way of framing this is to accept that most working relationships will decay, but you want the ability to quickly pick things up at some arbitrary point in the future. To enable that, I'd recommend that you have something interesting to say/share, and be able to show receipts. Maybe you published an app that got tens of thousands of users, started a cool YouTube channel, or started angel investing. Being able to show people what you did will make past relationships much warmer.